1. Field of the Invention
The present invention relates to the sealing of cable junctions when it is decided to form a gas-tight enclosure around the junction, and when the means for supplying that enclosure is an envelope of heat-shrinkable material. It is particularly, but not exclusively, concerned with the sealing of branch junctions of electric or communication cables.
2. Summary of the Prior Art
In UK patent application GB 2198594A, jointly in the names of ourselves and Fujikura Ltd., we described an arrangement for sealing cable junctions in which one or more insert parts were positioned between a pair of branch cables. The insert part had a block of heat-fusible material, and one or more flanges of heat-conductible material. The flanges each had a tongue which extended into the block. A heat-shrinkable envelope was then positioned around the branch cable, and the insert part(s) and the envelope was then shrunk by the application of heat. That heat caused the block material to fuse, which process was assisted by heat conduction via the tongues of the flange(s). Thus the space within the envelope, around the branch cables, was filled by fused block material, so that a seal was achieved. The flanges of the insert part also assisted in the positioning of the insert part, as they could be wrapped around the branch cables.
In GB 2198594A we described several embodiments of insert parts for achieving the above result. In that specification, we said that where the branch cables had a large diameter, it would be necessary to provide several insert parts to achieve the desired melting of the material of the blocks of those insert parts.
We also described another embodiment in which there was one block, but several flanges.
In all of these cases, the flange was a simple "T"-shape, with the leg of the "T" forming the tongue extending into the block for heat conduction.
We have now investigated further the problem of sealing junctions of very large cables, and it has been found that the provision of a plurality of insert parts, as described in 2198594A is not wholly satisfactory.